Field of the Invention
The present invention relates to a belt conveyance apparatus employed in an image forming apparatus of an electrophotographic method or of an electrostatic recording method, and an image forming apparatus including the belt conveyance apparatus.
Description of the Related Art
Conventionally, in an image forming apparatus employing an electrophotographic method and the like, an intermediate transfer member and an endless belt (hereinbelow, sometimes simply referred to as an belt) are employed. Onto the intermediate transfer member, a toner image to be transferred to a recording medium is temporarily transferred. The belt is used as a recording medium bearing member to convey a recording medium on which a toner image is transferred. Further, a belt may be used, for example, as a recording medium conveyance member for conveying a recording medium that contacts the intermediate transfer member at a transfer portion where a toner image is transferred from the intermediate transfer member to the recording medium.
A belt conveyance apparatus that conveys such a belt includes a belt and a plurality of support rollers around which the belt is wound. In the belt conveyance apparatus, a belt shift may occur due to the alignment deviation and the conveyance friction of the support rollers. In the belt shift, the belt is moved in a width direction, which is a direction substantially orthogonal to the belt conveyance direction (i.e., thrust direction).
Therefore, conventionally, in order to restrain the belt shift, a belt shift regulation means has been used. Examples of the belt shift regulation means include the following configurations. Specifically, at the end portions of inner peripheral surface side (i.e., back side) of the belt in a width direction, regulation ribs as receiving members are provided, regulation rollers (i.e., flanges) as regulation portions are provided at respective end portions of at least one support roller in a rotation axis direction. Then, the regulation ribs are brought into contact with the regulation roller to regulate the movement of the belt in the width direction.
In addition, there is discussed a technique for regulating bending of the belt generated due to the contact of the regulation rib with the regulation roller, and improving the effect of the belt shift regulation.
For example, Japanese Patent Application Laid-open No. 2002-132057 discusses a technique in which a biasing member for biasing the belt is provided at an opposing position of the regulation roller on an outer peripheral surface side (i.e., front surface) of the belt, in the belt shift regulation means including a regulation rib and a regulation roller.
In addition, Japanese Patent Application Laid-open No. 2009-42723 discusses following configurations. Specifically, in the belt shift regulation means in which an end portion of the belt as a regulation receiving member in a width direction is brought into contact with a contact portion as a regulation portion, a biasing member for biasing the belt in a thickness direction on a front surface side of the belt near the contact position and upstream side of the belt conveyance direction.
Further, Japanese Patent Application Laid-open No. 2005-070496 discusses a configuration in which a back up member is provided to support a belt from the back side of the belt.
Meanwhile, the belt conveyance apparatus including a belt with a relatively shorter peripheral length and a support roller with a small diameter is susceptible to the attitude change of the regulation rib. Therefore, as illustrated in FIG. 12, riding-on of a belt 201 may easily occur due to the rising of a regulation rib 202 over a regulation roller 203 when the belt 201 is moved to one side in a width direction of the belt 201. The reason will be described below.
In the example illustrated in FIG. 12, the regulation rib 202 is provided on the entire circumference of the belt 201 at both end portions of a back side thereof in a width direction, and a regulation roller (flange) 203 is provided on each end portion of a support roller 204 in a rotation axis direction. The regulation roller 203 includes an oblique surface (taper portion) at the end portion thereof. The oblique surface inclines to increase the diameter thereof as going up toward the center side of the rotation axis direction of the support roller 204. In addition, FIG. 12 is a cross sectional view illustrating vicinity of the support roller 204 and on the upstream side of the belt 201 in the conveyance direction.
For example, when the inner side of the belt conveyance apparatus becomes dirty due to scattering of developer or the like, it may cause a quality deterioration of an image or increase a shift amount of a belt. Therefore, to prevent entering of the developer and the like inside the belt conveyance apparatus, a scattering prevention member such as a fur brush may be provided at each end portion of back side of the belt in a width direction. The scattering prevention member may sometimes be provided to enter a stretching surface of the belt from the inside toward the outside of the belt. In this case, as illustrated in FIG. 13, the end portion of the belt 201 in the width direction is deformed by the scattering prevention member 205 to be expanded from the inside toward the outside, and it may cause the attitude of the regulation rib 202 to be unstable when the regulation rib 202 enters a regulation operation portion, which is the contact portion with the regulation roller 203. Further, when, on the upstream side of the support roller in which the regulation roller is provided in the conveyance direction of the belt, a support roller with an inverse crown shape (i.e., the external diameter at the center portion thereof is smaller than those at the end portions thereof in the rotation axis direction) is provided or a fur roller for cleaning the belt is provided, a similar disadvantage may occur. In addition, in a case of a belt with a relatively short peripheral length, the attitude of the regulation rib 202 is not easily corrected while the belt enters the contact portion with the regulation roller from the expanded position from the inside to the outside, as described above. As a result, the shift regulation of the belt may easily become unstable.
Further, as illustrated in FIG. 14, when the end portion of the belt 201 in the width direction is deformed to be pressed from the outside toward the inside, the attitude of the regulation rib 202 may become unstable when the belt 201 enters the regulation operation portion, which is the contact portion with the regulation roller 203 having a taper. This may occur in a case where a support roller in a normal crown shape (i.e., the external diameter at the center portion is larger than those at the end portions thereof in the rotation axis direction) is provided on the upstream side of the support roller in which the regulation roller is provided in the conveyance direction of the belt. Also in this case, since the attitude of the regulation rib may be changed, similarly as described above, in a case of a belt with a relatively short peripheral length, the belt shift regulation may become easily unstable.
Meanwhile, in order to make the belt shift regulation more secure, a solution to increase the thickness of the regulation rib may be conceivable. However, in the belt conveyance apparatus provided with a relatively short peripheral length and a support roller with a relatively small diameter, as the curvature of the belt is small, it is disadvantageous in terms of durability. Therefore, it may not be an effective solution.
There is a method for improving the belt shift regulation ability by biasing the end portion of the belt in the width direction from one side of the belt (i.e., the front surface side or the back surface side), as the above-described conventional technique.
However, for example, when a biasing member is disposed to press the position opposing the regulation roller, friction between the regulation roller and the regulation rib may become excessively large. As a result, a force may act in a direction to raise the regulation rib over the regulation roller, and the contact position of the regulation rib and the regulation roller moves near the outer periphery side of the regulation roller. As a result, riding-on may occur. Further, for example, in a case where the biasing member is disposed near the belt shift regulation operation portion and on the front surface side of the belt on the upstream side in the conveyance direction, the end portion of the belt in the conveyance direction may be pressed more than necessary from the outside toward the inside. Also in this case, similarly as described above, sufficient belt shift regulation cannot be achieved, and riding-on may occur.
In addition, the above-described problem may easily occur in a case of the belt conveyance apparatus including a belt with a relatively short peripheral length and a support roller with a relatively small diameter. However, the problem can generally occur to some degree or another with a belt conveyance apparatus.